I don't really follow what your point is.

But, developers will build what maximizes profits. They are just answering to wallets. If it was mostly the ultra-wealthy purchasing real estate (as it mostly was pre-WW2), then the developers will build what the ultra-wealthy want to spend their money on.

Post-WW2 saw the rise of the middle class and their ability to purchase homes. Especially with government-backed mortgages (FNMA, Freddie Mac, and etc). Most of the middle class would rather spend less on gorgeous architecture and get more square footage inside their home.